We at the virtualization team, have been creating copies of a virtual machine to use them as workstations that will be grouped into a domain. The only problem is that the original virtual machine was not syspreped and apparently this is creating problems joining the domain; this can be seen when new users can not log in the new virtual machine.
One quick and easy way that we have found helpful to fix this is changing the name of the computer (to avoid the duplicated name) and moving it to a temporary workgroup at the same time (we couldn't get to rename otherwise). Then we just made the computer reboot, and then moved it back to the domain, and reboot again. After that, it worked just fine.